Extracts prepared according to the processes of the prior art, particularly the processes described in FR-A-2,092,743 and FR-A-2,372,823 concerning Vitis vinifera, the process described in FR 1,427,100 and in U.S. Pat. No. 4,698,360 concerning maritime pine, proved to contain, in addition to the oligomers of polymerization degree 2 to 7, condensation products of higher molecular weights (in spite of a treatment with a sodium chloride saturated aqueous solution) and, above all, monomers in the not negligible proportions of 20 to 30% by weight. These monomers are considered undesired substances. A medicinal proprietary product containing as the active ingredient only catechin, has been withdrawn from the market because of side effects.
Some side effects of flavonoids have been reported see Jaeger et al "Side Effects of Flavonoids in Medical Practice". Plant Flavonoids in Biology and Medicine II: Biochemical, Cellular, and Medicinal Properties, pages 379-394 (1988).
British patent 1,541,469 describes a process consisting of extracting the organic matter with an acetone-water mixture containing 3-4 volumes of acetone to one volume of water. The patent states that all the oligomers are extracted but no mention is made with respect to the monomers.
The process of French 2,092,743 also involves the use of an aqueous ketone. Also, this patent alleges complete extraction of the oligomers but no mention is made of the monomers.
Although a number of processes for the extraction of flavanolic oligomers or similar substances present in vegetable material have already been described (see, for instance, FR Patents 968,589, 1,036,922 and 1,427,100 and GB Patent 1,541,469), it has not been simple to obtain on an industrial scale and in economically acceptable yields extracts almost completely free from monomers, with no remarkable losses or alterations in the dimers and the other oligomers, whose physico-chemical characteristics are clearly similar.